Measuring laser light transmissivity in a to-be-welded region of a work piece

ABSTRACT

Methods for measuring laser light transmissivity of a specific position in a work piece prior to the work piece undergoing laser welding at the specific position with a laser beam having a specific welding wavelength. To obtain a baseline measurement reading, a laser light source projects a laser beam at the welding wavelength directly into a detector. Thereafter, the work piece becomes suspended between the laser light source and detector whereby an output of the detector now corresponds to a work piece measurement reading. Differences between the two readings reveal whether the work piece will yield a satisfactory weld at the specific position when later welded by a laser beam at the welding wavelength. Preferred work pieces include inkjet printhead lids and bodies.

This application claims priority as a continuation application of U.S.application Ser. No. 11/093,971 filed on Mar. 30, 2005 now U.S. Pat. No.6,980,296, entitled “Measuring Laser Light Transmissivity in aTo-Be-Welded Region of a Work Piece,” in turn claiming priority as adivision of an application by the same name having Ser. No. 10/359,470and filed on Jan. 30, 2003 now abandoned.

FIELD OF THE INVENTION

The present invention relates to measuring light transmissivity of awork piece. In particular, it relates to measuring laser lighttransmissivity of a specific position in a work piece prior to the workpiece undergoing laser welding at that specific position. Even moreparticularly, it relates to assessing whether the work piece will yielda satisfactory weld at the specific location when welded by a laser beamirradiated at a specific welding wavelength. Work pieces may compriseinkjet printhead lids and bodies.

BACKGROUND OF THE INVENTION

The art of measuring light transmissivity in a work piece is relativelywell known. In general, light from a source passes from a front side ofthe work piece to the backside where a detector collects it. Thedifference between the light irradiated towards the work piece and thelight that actually passes through the work piece, as collected by thedetector, corresponds to the work piece transmissivity.

Problems arise, however, because the light source, often a white lightsource, illuminates the front of the work piece with multiplewavelengths while the detector only collects light at its tunedwavelength. This can unnecessarily limit measurement of multiplewavelengths to incorporating multiple detectors. Additionally, typicalcommercial transmissivity measurement devices lack sufficientirradiation power to penetrate work pieces and project light to backsidedetectors when the work pieces embody other than visibly clearcompositions. Traditional visibly clear compositions include glass,quartz, polycarbonate, polystyrene, and the like. They usually also lacksufficient power to project light through work pieces, such as highimpact polystyrene and polyester having typically low transmissivitycharacteristics.

Accordingly, the arts for measuring light transmissivity desiresolutions for overcoming the aforementioned and other problems.

Numerous reasons exist for understanding light transmissivity in a workpiece. For example, consider instances when two work pieces undergolaser welding. As background, first and second work pieces become weldedto one another by way of a fixed or sweeping irradiated beam of laserlight. As is known, the beam passes through the first work piece, whichis transparent to laser light, where it gets absorbed by the second workpiece, which is laser light absorbent. As the beam irradiates, the weldinterface heats-up which causes the adjoining surfaces of the workpieces to melt. Upon cooling, the two work pieces meld together as one.

Yet, if the first work piece prevents sufficient amounts of laser lightfrom reaching the weld interface, poor welding (underweld) results.Further, if the first work piece absorbs too much energy, the first workpiece may overheat and/or suffer material degradation potentiallycausing poor weld appearance or unsatisfactory welds. Numerousparameters contribute to the absorption and transmission characteristicsof a work piece including, but not limited to, laser wavelength,incident angle of the laser beam during welding, surface roughness ofthe work piece, temperature of the work pieces, thickness/dimensions ofthe work piece, composition of the work piece and, in instance when workpieces comprise plastics, additives such as flame retardants,plasticizers, fillers and colorants.

When the material properties and laser properties become fixed in agiven system, however, the transmission rate of the laser through a workpiece follows the well known Beer-Lambert Law, specifically:I/Io=e^((−sx)); where Io is the intensity of the light source incidenton the work piece, I is the intensity of the light after passing throughthe work piece, x is the thickness of the work piece, and s is the totalextinction coefficient which, in turn, is the work piece lightscattering coefficient plus the work piece light absorption coefficient.Accordingly, the transmissivity of the work piece constitutes animportant variable (underscored by the ratio I/I_(o)) in lighttransmission rates.

As such, those skilled in the laser welding arts will appreciate thathaving an ability to assess, predict or otherwise identify a laser lighttransmissivity characteristic of a work piece before the piece undergoeswelding will likely significantly decrease failure weld-rates into-be-welded work pieces.

Accordingly, a need exists in the laser welding arts for efficaciouslypredicting and identifying laser light transmissivity in to-be-weldedregions of a work piece.

Regarding the technology of inkjet printing, it too is relatively wellknown. In general, an image is produced by emitting ink drops from aninkjet printhead at precise moments such that they impact a printmedium, such as a sheet of paper, at a desired location. The printheadis supported by a movable print carriage within a device, such as aninkjet printer, and is caused to reciprocate relative to an advancingprint medium and emit ink drops at such times pursuant to commands of amicroprocessor or other controller. The timing of the ink drop emissionscorresponds to a pattern of pixels of the image being printed. Otherthan printers, familiar devices incorporating inkjet technology includefax machines, all-in-ones, photo printers, and graphics plotters, toname a few.

A conventional thermal inkjet printhead includes access to a local orremote supply of color or mono ink, a heater chip, a nozzle or orificeplate attached to the heater chip, and an input/output connector, suchas a tape automated bond (TAB) circuit, for electrically connecting theheater chip to the printer during use. The heater chip, in turn,typically includes a plurality of thin film resistors or heatersfabricated by deposition, masking and etching techniques on a substratesuch as silicon.

To print or emit a single drop of ink, an individual heater is uniquelyaddressed with a small amount of current to rapidly heat a small volumeof ink. This causes the ink to vaporize in a local ink chamber (betweenthe heater and nozzle plate) and be ejected through and projected by thenozzle plate towards the print medium.

During manufacturing of the printheads, a printhead body gets stuffedwith a back pressure device, such as a foam insert, and saturated withmono or color ink. A lid welds to the body via ultrasonic vibration.This, however, sometimes causes cracks in the heater chip, introducesand entrains air bubbles in the ink and compromises overall integrity.

Even further, as demands for higher resolution and increased printingspeed continue, heater chips become engineered with more complex anddenser heater configurations which raises printhead costs.Simultaneously, the heater chips become smaller and flimsier to savesilicon costs. Thus, as printheads evolve, a need exists to controloverall costs and to reliably and consistently manufacture a printheadwithout causing cracking of the ever valuable heater chip.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying theprinciples and teachings associated with the hereinafter describedmeasurement of laser light transmissivity in a to-be-welded region of awork piece.

In one embodiment, the invention teaches methods for measuring laserlight transmissivity of a specific position in a work piece prior to thework piece undergoing laser welding at the specific position with alaser beam having a specific welding wavelength. As a first step, theinvention teaches obtaining a baseline measurement reading between alaser light source and a detector by projecting a laser beam, at theto-be-welded welding wavelength, directly into the detector. The workpiece becomes suspended between the laser light source and detector suchthat the laser beam at the welding wavelength passes through the workpiece in the vicinity of the specific to-be-welded position and into thedetector. An output of the detector corresponds to a work piecemeasurement reading. Differences between the two readings reveal whetherthe work piece will yield a satisfactory weld at the specific positionwhen later welded by a laser beam at the welding wavelength. Theinvention also contemplates filters, mirrors, collimators, lenses andthe like in the optical path between the light source and the detector.

In another aspect of the invention, a substantially bottomless traysuspends work pieces between the laser light source and the detectorsuch that when the work piece becomes indexed to a new position, thetray never interferes with the beam of laser light. An X-Y motion tablein combination with a stepper motor preferably provides the impetus forindexing.

In still another aspect, indexing motion and laser light transmissivityreadings occur in patterns substantially paralleling a periphery of thework piece.

Inkjet printhead lids and bodies, laser welded together at specificpositions having undergone laser light transmissivity measurements atspecific welding wavelengths, and printers containing the printheads arealso disclosed.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in the description which follows,and in part will become apparent to those of ordinary skill in the artby reference to the following description of the invention andreferenced drawings or by practice of the invention. The aspects,advantages, and features of the invention are realized and attained bymeans of the instrumentalities, procedures, and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view in accordance with the teachings of thepresent invention of an apparatus for measuring laser lighttransmissivity in a to-be-welded region of a work piece;

FIG. 2A is a diagrammatic view in accordance with the teachings of thepresent invention of a tray for suspending a work piece between a laserlight source and a detector for use with the apparatus of FIG. 1;

FIG. 2B is a cross-section view in accordance with the teachings of thepresent invention of the to-be-welded work piece of FIG. 2A after beingplaced in the tray;

FIG. 2C is a planar view in accordance with the teachings of the presentinvention of the to-be-welded work piece held in the tray of FIG. 2Bhaving pluralities of laser light transmissivity measurement positionsindicated;

FIG. 3 is a diagrammatic view in accordance with the teachings of thepresent invention of laser light projected through a work piece andcollected by a detector for use with the apparatus of FIG. 1;

FIG. 4 is a graph in accordance with the teachings of the presentinvention of measured laser light transmissivity of a work piece plottedagainst discrete measurement positions;

FIG. 5 is a perspective view in accordance with the teachings of thepresent invention of an inkjet printhead with a laser lighttransmissivity measured inkjet lid laser welded to an inkjet body; and

FIG. 6 is a perspective view in accordance with the teachings of thepresent invention of an inkjet printer for housing an inkjet printheadwith a laser light transmissivity measured inkjet lid laser welded to aninkjet body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration, specific embodiments inwhich the inventions may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process or other changes may be made without departingfrom the scope of the present invention. As a matter of conventionherein, direction arrows and lines in-between serve to showinterconnections between devices. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined only by the appended claims and theirequivalents. In accordance with the present invention, we hereinafterdescribe measurement of laser light transmissivity in a to-be-weldedregion of a work piece.

With reference to FIG. 1, an apparatus for measuring lighttransmissivity is shown generally as 10. The apparatus includes acomputing system environment 12 having, at one end thereof,bi-directional communication with a laser diode power controller 14 anda laser diode temperature controller 16. In a preferred embodiment, thepower controller embodies a Thorlabs Inc., LDC2000 2A laser diodecontroller while the temperature controller embodies a Thorlabs Inc.,TEC2000 TEC controller. The computing system environment embodies ageneral or specific purpose computer with attendant processors, memory,monitors, input devices, network connections, peripheral devices,application programs, connections to intranets and internets and thelike.

At the other end, the computing system environment bi-directionallycouples with a laser light source structure 20, a motion table 22 and adetector structure 24. In more detail, the laser light source structure20 includes a laser mount 26, a laser diode 28 and collimating andfocusing optics 30. In a preferred embodiment, the laser mount includesa Thorlabs Inc., TCLDM3 TEC LD mount while the diode includes a 1200 mW,T0-3 package from Coherent Laser Diode, S-81-1200C-100-Q. Thecollimating and focusing optics comprise one or some of Thorlabs Inc.'s:C230TM-B, 600-1500 nm Moderate NA Optics; C260TM-B 600-1500 nm 0.15 NAAR coating; E09 RMS Microscope Objective Adapter Extension Tube; OpticsAdapter S1TM09; CP02 Threaded Cage Plate; SM1A3 Microscope Objective toSM1 Adapter; ER4 0876-001 REV B, Extension Rod 4 inch (×4); and SM1RRRetaining Ring. In other embodiments, the laser diode represents an 810nm wavelength aluminum gallium arsenide (AlGaAs) semiconductor laserhaving a laser power of about 1000 mW. Still other embodiments include,but are not limited to, other types of continuous wave lasers withsimilar power intensities such as semiconductor lasers based on IndiumGallium Arsenide (InGaAs) with wavelengths of 940-990 nm and AluminumGallium Indium Phosphide (AlGaInP) with wavelengths of 630-680 nm, solidstate lasers such as lamp pumped Neodymium-doped Yttrium Aluminum Garnet(Nd:YAG) with a wavelength of 1064 nm and diode pumped Neodymium-dopedYttrium Aluminum Garnet (Nd:YAG) with a wavelength of 1064 nm orsolid-state, gas, excimer, dye, ruby or semiconductor lasers or argonfluoride, krypton fluoride, nitrogen, argon (blue or green), helium neon(blue or green), rhodamine 6G dye (tunable), CrAlO₃, NIR or carbondioxide (FIR) laser types or other. The laser diodes of the laser lightstructure may additionally have labels of class I, I.A, II, IIIA, IIIB,or IV as those are well understood in the art.

The motion table 22 has an elevation arm 32 that allows insertion of awork piece 50 into an optical path (dashed straight line between laserand detector structures) at a position above the laser light sourcestructure. An offset arm 34 of the motion table provides lateral controlwith motion controlled in a region away (action arrow A) from theoptical path. A microcontroller 36 and stepper motor 38 provide theelectrical and mechanical impetus to the motion table preferably frominstructions originating in the computing system environment. In oneembodiment, the motion table 22 has X-Y positioning. In otherembodiments, the motion table has X-Y-Z motion, theta motion, angularmotion, linear motion or combinations of some or all of the foregoing.

The detector structure 24 includes a photodetector 40 and an optionalfilter 42. In one embodiment, the photodetector is a Thorlabs Inc., DET110 350-1100 nm Photodetector while the filter is an NE20A D-2.0 MountedAbsorptive Natural Density Filter.

A support frame 44 a, 44 b extending from a base 46 provides a platformupon which the laser light source structure 20, the motion table 22 anddetector structure 24 commonly connect. In this manner, the framemaintains a common reference point and distances and angles between allstructures are known or can be measured. In a preferred embodiment, theframe fixes the laser light source and detector structures relative toone another.

The apparatus 10 may additionally include various mechanical/electricalinterlocks (not shown) between any or all of the foregoing structures tomeet or exceed federal safety requirements. In one embodiment, the base46, the frame 44 and all structures connected thereto reside within alight safe enclosure (not shown) according to ANSI standard Z136.1, forexample. Other apparatus structures include suitable power sources (notshown) to power some or all of the foregoing.

During use, the apparatus 10 works to emanate and project a laserbeam(s) along the optical path from the laser light source structure 20to a front side 52 of the work piece. In turn, the laser beam(s) passes,or not, through the work piece 50 to a backside 54 and into thedetector. Signals output from the detector become transferred to thecomputing system environment where a user/software analyzes them forlight transmissivity characteristics of the work piece.

More specifically, and as a preliminary matter, the work piece 50 isloaded in the tray 70 at a home position, which is around 200 mm awayfrom the laser light source structure 20 and the detector structure 24.A safety door of the light safe enclosure shuts and the apparatusobtains a baseline measurement reading by originating and projecting alaser beam along the optical path in a direct line from the light sourcestructure to the detector structure without passing the laser beamthrough the work piece.

Thereafter, the work piece 50 is inserted into the optical path bymovement from the home position to a starting position between the laserlight source and detector structures by the X-Y motion table. The laserbeam projects toward/through the work piece and light collected from thebackside 54 by the detector corresponds to a work piece measurementreading. This process repeats, as described in greater detail below,such that pluralities of work piece measurement readings are obtained.Differences between the baseline measurement and the work piecemeasurement readings reveal the laser light transmissivity of the workpiece. In a preferred embodiment, voltage outputs of the detectorstructure 24 have a mathematical relationship in terms of transmittedlight T(t) such that T(t)=Y(t)/X; where Y is the detected intensity attime t and X is the baseline measurement reading. A mean transmissivityvalue can be calculated by summing the above equation for the durationof a given time interval.

As an example, consider a baseline measurement reading having sometrivial output of about 10 volts. Next consider a first work piecemeasurement reading of about 7 volts. In percentages, the laser lighttransmissivity of the work piece at that work piece position is about70%. Then, as additional work piece measurement readings are taken,preferably at other work piece positions, information about the workpiece transmissivity is obtained and can be graphed as shownrepresentatively in FIG. 4.

As readily identifiable in the graph, laser light transmissivitypreferably stays within a zone B between 50 and 100 percent, forexample. Yet, at measurement positions 1000 and 4000, laser lighttransmissivity drops to much lower percentage levels. Over time, andfrom knowledge learned by testing and identifying acceptable laser weldsof work pieces, users can set some minimum acceptable level, such asdashed line 60, that readily identifies whether the work piece undertest in apparatus 10 will yield satisfactory weld results. Users willset their own criteria for distinguishing satisfactory welds fromunsatisfactory ones. The criteria may include, but are not limited to,how many aberrations such as those found at positions 1000/4000 a weldcan withstand or how high a laser light transmissivity percentage onaverage, total, or other will yield an acceptable result. For thoroughdisclosure, the representative readings taken at work piece measurementpositions 1000 and 4000 were found in one actual reduction to practiceto correspond to impurities, such as carbon or steel, in the compositionof the work piece in instances when the work piece comprised a plasticformed in an injection molding chamber.

It should be appreciated, however, that testing the work piece inapparatus 10 (FIG. 1) for transmissivity characteristics is performed ata laser wavelength corresponding substantially to the specific laserwavelength used during laser welding. Even more preferably, testing ofthe work pieces in apparatus 10 occurs with the same exact laser lightsource structure 20 used during subsequent laser welding operations ofthe work piece. In this manner, users can even more accurately predictand identify a direct correlation between transmissivity andsatisfactory welds.

To physically introduce the work piece between the laser light sourceand detector structures, the offset arm 34 having the work piece 50therewith rotates or otherwise moves into the optical path. Withreference to FIGS. 2A and 2B, a preferred structure for holding the workpiece at a terminal end of the offset arm includes a tray 70.

As shown, the tray 70 has a plurality of walls 72(a-d) that form a framearound a periphery 56 of the work piece 50. A perimeter distance of aninterior 74 of the walls is slightly larger than the perimeter distanceof the periphery 56. In this manner, a user may easily insert the workpiece into the tray and the tray will maintain the work piece in a fixedposition relative thereto. Near a bottom 75(a-d) of the walls, a ledge76(a-d) juts out slightly such that when the work piece is inserted intothe tray, the front side 52 surface of the work piece rests in contacton a top surface 80(a-d) thereof. In one embodiment, the ledge juts outa distance d of about 5/1000^(th) of an inch.

Those skilled in the art should observe that despite a slight ledge, thetray otherwise has a substantially bottomless quality. In this manner,when the laser light source structure 20 (FIG. 1) projects laser beamsof light towards, and perhaps through the work piece, the substantiallybottomless tray 70 suspends the work piece between the laser lightsource and detector structures such that nearly the entirety of thefront side 52 surface of the work piece receives direct laser lightwithout any interference from the tray. Preferably, in a direct line(e.g., optical path, dashed line, FIG. 1) between the laser light sourcestructure 20 and the detector structure 24, no portion of the tray evercrosses the line.

The tray 70 can affix to the offset arm at any variety of positions,such as outside 73 of wall 72 a, by adhesives, clamps, fasteners orother or by integral formation therewith.

As depicted, the work piece 50 has a thickness t less than a height h ofthe walls so that it nests within the tray. Those skilled in the artwill appreciate, however, that the work piece may have other thicknessesthat extend beyond or exist substantially parallel to a top 82(a-d) ofthe walls and this invention embraces all varieties.

To have even greater usefulness, the positions, in which transmissivitymeasurements are taken, should correspond directly to the positions thatwill later become laser welded. With reference to FIG. 2C, a pluralityof such later-welded work piece positions are shown generally as aplurality of discrete dots (with two labeled 90-1 and 90-4) arranged ina substantially rectangular pattern (although only shown on three sidesof the work piece 50 with a dashed line arrow C indicating continuationof the pattern) substantially paralleling a periphery 56 of the workpiece. Thus, when users take measurements they do so at the positionsindicated by the pattern.

The invention, however, should not be considered so narrowly to precludeother patterns of work piece positions. Thus, the invention contemplatesother patterns and user need generally dictates them. For example, theinvention finds equal utility with round, triangular, square, linear,spotted and random or other patterns or patterns of continual lines ofpositions instead of discrete positions or combinations thereof.

In one actual embodiment, the invention found utility with about 12,000work piece positions in a substantially rectangular pattern with about ½of 1/10000^(th) of an inch between positions. The measurements occurredat the work piece positions in the following manner: i) introduce andsuspend the work piece in the tray at a home position away from theoptical path; ii) project a laser beam directly from the light source tothe detector structure; iii) obtain a baseline measurement reading; (iv)energize stepping motor to stepwise control movement of the tray andwork piece to the starting position between the light source anddetector structures directly in the optical path; v) obtain a work piecemeasurement reading by passing the laser beam (which is continuous on,but not necessarily required to be) from the light source structure intothe work piece and observing/recording the output of the detectorstructure; (vi) energize the stepping motor to stepwise control movementof the tray; (vii) index the tray 70 and work piece 50 such that thenext work piece position is in the optical path; (viii) repeat steps(v)-(viii) until an entirety of the work piece is measured; ix) stop thelaser beam from projecting; and x) return tray 70 and work piece to thehome position by indexing the stepping motor. The work piece embodied asubstantially rectangular solid plastic composition of Noryl Brand TN300 having a thickness of about 2 mm and a length and width of about 50mm and 25 mm, respectively.

With reference to FIG. 3, the invention presents a more detailedillustration of a preferred optical path for use in the apparatus 10 ofFIG. 1. In particular, laser diode 28 in combination with a collimatinglens 100 and focusing lens 102 projects a laser beam 104 from the laserlight source structure towards a front side 52 of the work piece 50. Thedetector structure collects transmitted laser light 106 from a back side54 of the work piece with assistance from a converging lens 108, filter42 and photodetector 40. In other embodiments, the optical pathoptionally includes additional lenses, filters collimators or otheroptical elements, such as mirrors, fiber optic strands, scanningstructures or the like.

Finally, since the invention herein contemplates the work piece as aninkjet printhead lid or body, the remaining description relates tospecific work piece compositions and their arrangement as part of alaser welded printhead lid/body.

With reference to FIG. 5, a printhead of the present invention is showngenerally as 101. The printhead 101 has a housing 121 formed of a body161 and a lid 160 laser welded together by a laser beam at a weldinglaser wavelength at a specific work piece position at a time after thelid has its work piece position measured for laser light transmissivityat the specified welding laser wavelength. In one preferred embodiment,the lid comprises a laser transparent material having a composition ofpolyphenylene ether plus polystyrene while the body comprises a laserabsorbing material also having a composition of polyphenylene ether pluspolystyrene. Although shown generally as a rectangular solid, thehousing shape varies and depends upon the external device that carriesor contains the printhead. The housing has at least one compartment,internal thereto, for holding an initial or refillable supply of ink anda structure, such as a foam insert, lung or other, for maintainingappropriate backpressure in the inkjet printhead during use. In oneembodiment, the internal compartment includes three chambers forcontaining three supplies of ink, especially cyan, magenta and yellowink. In other embodiments, the compartment may contain black ink,photo-ink and/or plurals of cyan, magenta or yellow ink. It will beappreciated that fluid connections (not shown) may exist to connect thecompartment(s) to a remote source of ink.

A portion 191 of a tape automated bond (TAB) circuit 201 adheres to onesurface 181 of the housing while another portion 211 adheres to anothersurface 221. As shown, the two surfaces 181, 221 exist perpendicularlyto one another about an edge 231.

The TAB circuit 201 has a plurality of input/output (I/O) connectors 241fabricated thereon for electrically connecting a heater chip 251 to anexternal device, such as a printer, fax machine, copier, photo-printer,plotter, all-in-one, etc., during use. Pluralities of electricalconductors 261 exist on the TAB circuit 201 to electrically connect andshort the I/O connectors 241 to the bond pads 281 of the heater chip 251and various manufacturing techniques are known for facilitating suchconnections. It will be appreciated that while eight I/O connectors 241,eight electrical conductors 261 and eight bond pads 281 are shown, anynumber are embraced herein. It is also to be appreciated that suchnumber of connectors, conductors and bond pads may not be equal to oneanother.

The heater chip 251 contains at least one ink via 321 that fluidlyconnects to a supply of ink internal to the housing. During printheadmanufacturing, the heater chip 251 preferably attaches to the housingwith any of a variety of adhesives, epoxies, etc. well known in the art.As shown, the heater chip contains two columns of heaters on either sideof via 321. For simplicity in this crowded figure, dots depict theheaters in the columns. It will be appreciated that the heaters of theheater chip preferably become formed as a series of thin film layersmade via growth, deposition, masking, photolithography and/or etching orother processing steps. A nozzle plate with pluralities of nozzle holes,not shown, adheres over the heater chip such that the nozzle holes alignwith the heaters.

With reference to FIG. 6, an external device, in the form of an inkjetprinter, for containing the printhead 101 is shown generally as 401. Theprinter 401 includes a carriage 421 having a plurality of slots 441 forcontaining one or more printheads. The carriage 421 is caused toreciprocate (via an output 591 of a controller 571) along a shaft 481above a print zone 461 by a motive force supplied to a drive belt 501 asis well known in the art. The reciprocation of the carriage 421 isperformed relative to a print medium, such as a sheet of paper 521, thatis advanced in the printer 401 along a paper path from an input tray541, through the print zone 461, to an output tray 561.

In the print zone, the carriage 421 reciprocates in the ReciprocatingDirection generally perpendicularly to the paper Advance Direction asshown by the arrows. Ink drops from the printheads (FIG. 5) are causedto be ejected from the heater chip at such times pursuant to commands ofa printer microprocessor or other controller 571. The timing of the inkdrop emissions corresponds to a pattern of pixels of the image beingprinted. Often times, such patterns are generated in deviceselectrically connected to the controller (via Ext. input) that areexternal to the printer such as a computer, a scanner, a camera, avisual display unit, a personal data assistant, or other.

To print or emit a single drop of ink, the heaters (the dots of FIG. 5)are uniquely addressed with a small amount of current to rapidly heat asmall volume of ink. This causes the ink to vaporize in a local inkchamber and be ejected through, and projected by, a nozzle plate towardsthe print medium.

A control panel 581 having user selection interface 601 may also provideinput 621 to the controller 571 to enable additional printercapabilities and robustness.

As described herein, the term inkjet printhead may in addition tothermal technology include piezoelectric technology, or other, and mayembody a side-shooter structure instead of the head-shooter structureshown. Finally, since the to-be-welded work piece described above mayembody an inkjet printhead lid and/or body and since laser weldingimparts essentially no vibratory motion in the work pieces, unlikeultrasonic welding, less cracking of the heater chip occurs and less airbecomes entrained in the ink during printhead manufacturing.

The foregoing description is presented for purposes of illustration anddescription of the various aspects of the invention. The descriptionsare not intended to be exhaustive or to limit the invention to theprecise form disclosed. The embodiments described above were chosen toprovide the best illustration of the principles of the invention and itspractical application to thereby enable one of ordinary skill in the artto utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchmodifications and variations are within the scope of the invention asdetermined by the appended claims when interpreted in accordance withthe breadth to which they are fairly, legally and equitably entitled.

1. A method for measuring laser light transmissivity before laserwelding, comprising: introducing a work piece that is to undergo laserwelding at a specific laser wavelength a work piece position between alaser light source and a detector; without cutting or welding said workpiece, passing a laser beam at said wavelength from said laser lightsource through said work piece in a vicinity of said work piece positionand into said detector to obtain a work piece measurement reading; andbased upon said reading, assessing whether said work piece willsatisfactorily undergo subsequent laser welding to another work piece atsaid work piece position at said wavelength.
 2. The method of claim 1,further including stepwise controlling movement of said work piecebetween said laser light source and said detector.
 3. The method ofclaim 1, further including projecting said laser beam at said wavelengthfrom said laser light source into said detector without passing throughsaid work piece to obtain a baseline measurement reading.
 4. The methodof claim 1, wherein said introducing further includes suspending saidwork piece between said laser light source and said detector.
 5. Themethod of claim 4, wherein said suspending further includes positioningsaid work piece in a substantially bottomless tray.
 6. The method ofclaim 1, further including laser welding said work piece to an inkjetprinthead body at said work piece position.
 7. The method of claim 1,wherein said assessing further includes plotting said measurementreading versus said work piece position.
 8. The method of claim 1,wherein said assessing further includes determining whether saidmeasurement reading is above a predetermined minimum acceptable level.9. A method for measuring laser light transmissivity in a work piecebefore laser welding said work piece to another work piece, comprising:introducing said work piece that is to undergo laser welding at aspecific laser wavelength at a plurality of work piece positions in anoptical path between a laser light source and a detector; withoutcutting or welding said work piece, passing a laser beam at saidwavelength through said work piece in a vicinity of said work piecepositions to obtain a plurality of work piece measurement readings; andbased upon said measurement readings, assessing whether said work piecewill satisfactorily undergo subsequent laser welding to said anotherwork piece at said work piece positions at said wavelength.
 10. Themethod of claim 9, further including stepwise controlling movement ofsaid work piece between said laser light source and said detector. 11.The method of claim 9, wherein said passing said laser beam furtherincludes repeatedly and discretely passing a beam of laser light throughsaid work piece.
 12. The method of claim 9, wherein said passing saidlaser beam further includes continually passing a beam of laser lightthrough said work piece.
 13. The method of claim 9, further includingprojecting said laser beam at said wavelength from said laser lightsource into said detector without passing through said work piece toobtain a baseline measurement reading.
 14. The method of claim 9,wherein said assessing further includes plotting said measurementreadings versus said work piece positions.
 15. The method of claim 14,wherein said assessing further includes determining whether a sufficientpercentage of said measurement readings are above a predeterminedminimum acceptable level.